The present invention concerns improvements to the mechanical seal, and agitating device and process using same.
Mechanical seals are often used as a typical seal structure for use in rotary apparatuses. For example, if fluid is agitated in the agitating tank, rotary blades built in the agitating tank are rotated by means of a revolving shaft with its leading end portion received by the agitating tank, and the perimeter of the revolving shaft is rendered reliably liquidproof by the mechanical seal.
The pressure between the sliding faces of sliding rings in the mechanical seal greatly affects the sealability and the resistance to rotation of the revolving shaft. This pressure tends to fluctuate under the influence of various factors such as pressures of sealing fluid, spring, flushing liquid, etc.
More specifically, the flushing fluid is intended to be introduced into a seal box (stuffing box) as in order to cool the sliding rings. As the pressure of the flushing fluid increases, the pressure between the sliding faces tends to decrease. In this connection, for example, if the rotary speed of the revolving shaft is needed to increase, there is a limit to speeding up of the revolving shaft in terms of the flushing liquid. More specifically, it is necessary to increase the flow rate of flushing liquid for the purpose of cooling of the sliding rings as the revolving shaft is turned at higher speeds. The more the flow rate of flushing liquid, the higher the pressure of the flushing liquid, followed by the decrease of the pressure between the sliding faces. Since lowering of the pressure between the sliding faces may create liquid leaks, there would inevitably be a limit to the speed up of the revolving shaft in association of the flow rate of flushing liquid or the fluid pressure.
Desired pressure between the sliding faces is dependent on the pressures of a seal fluid used. Therefore, the mechanical seal is designed based on the pressure of the seal liquid being used that has been set within a predetermined range. If said pressure happens to deviate from the range, there would occur harmful effects such as liquid leaks, or increase of resistance to rotation.
In order to cope with such a problem, as the case may be, pressure-equalizing tubes are used to change the pressure of flushing liquid in response to the pressure change of seal fluid. However, such a solution needs to establish complicated requirements in connection with the rotary speed of the revolving shaft.
Many mechanical seals incorporate a spring acting to bias the sliding rings. The strength of said spring is designed in consideration of manifold factors. So, theoretically, the pressure between the sliding faces can be altered by changing the strength of spring. However, it is awfully difficult to change the spring strength into an adequate value in the mechanical seal fabricated from specific design. Particularly, it is safe to say that in operation, it is impossible to manipulate the spring in its inherent elasticity on the sliding rings.
On the other hand, nowadays, in the drugs or food industry, sterilization treatment must often be performed concurrently with the agitation treatment for fluid. In such a case, it is also necessary to clean and sterilize the mechanical seal in order to keep the interior of the agitating tank sterilized. In the past, such cleaning and sterilization operations had to be carried out after the mechanical seal had been disassembled. However, processes for performing cleaning or sterilization without disassembly, which are called CIP (cleaning in position) or SIP (sterilization in position) are becoming the mainstreams of today.
For example, Japanese Patent Publication No. 6-89872 proposed a process for keeping the sterilization medium constituted by a section surrounding the mechanical seal portion sterilized by subjecting this sterilization medium to sterilization by steam or introducing sterilized water into said medium.
However, said proposal has a problem that because the sliding faces of sliding rings in the mechanical seal portion are subjected to force fit by a predetermined pressure, steam never reaches the gap between the sliding faces, with the result that a complete sterilization can not be made. In cleaning only or in conjunction with sterilization also lies a similar problem.
Cleaning liquid, sterilization liquid, liquefied steam (water), or cooling liquid used for cooling the mechanical seal in operation may partially collect in the passage. Such a liquid pool is called xe2x80x9ccold pointxe2x80x9d. Liquid gathered in this cold point may be an obstacle to reliable sterilization at the time when further sterlization takes place. In particular, the sterilization requirement on the basis of SIP needs passage of pure steam at a temperature higher than 121xc2x0 C. for 20 minutes in order to sterilize the mechanical seal portion. However, if the introduced pure steam gets in touch with liquid such as water gathered in the cold point, the temperature of the pure steam will go down, thereby failing to meet said sterilization requirement.
An object of the present invention is the provision of a mechanical seal that may readily control the pressure between the sliding faces of sliding rings, and an agitating device and process using the mechanical seal.
Further object of the present invention is to widen the pressure range for seal liquid and the range of the rotary speed of revolving shaft in which the mechanical seal can be suitably used, by the provision of the mechanical seal enabling the pressure control between the sliding faces.
Further object of the present invention is to provide a mechanical seal that may control the pressure between the sliding faces in operation.
Another object of the present invention is to provide a mechanical seal, and an agitating device and process using same, in which a reliable cooling and sterilization of the sliding faces of sliding rings in the mechanical seal portion can also take place.
Further object of the present invention is to provide a mechanical seal, and an agitating device and process using same, in which a reliable sterilization may be carried out without creation of liquid pools (cold points) which constitute an obstacle, especially, to sterilization through steam.
A first invention of the present application provides a mechanical seal for building a liquid seal between a plurality of sliding rings 2, 3 opposed and rotatable relatively, namely sliding faces 2a, 3a of said opposed sliding rings 2, 3, characterized in that it includes controlling mechanisms 6, 53 of controlling force to bias at least one 3 of these sliding rings 2, 3 against the other one 2, so that the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings may be controlled. Said controlling mechanism is capable of controlling the pressure or the gap between the sliding faces 2a, 3a regardless of the pressure of seal fluid or flushing liquid, or within the range wider than the range in which the pressure between the sliding faces may be changed by the seal fluid or flushing liquid.
A second invention of the present application provides the mechanical seal in accordance with the first invention, characterized in that at least one sliding ring 3 is pressed against the other sliding ring 2 by an elastic body, and that said controlling mechanisms 6, 53 act to control the biassing force by applying force in the direction in which the pressing force due to said elastic body goes, or counter to said pressing force. In many conventional mechanical seals, one sliding ring 3 is pressed toward another sliding ring 2 by means of the elastic body. In this invention, the pressure or the gap between the sliding faces 2a, 3a can be controlled by applying force in the direction in which the pressing force goes or counter to said direction.
A third invention of the present application provides the mechanical seal in accordance with the first or second invention, characterized in that said controlling mechanisms 6, 53 serve to apply positive or negative pressure of control liquid to at least one sliding ring 3 in an axial direction of the revolving shaft of the mechanical seal. In this invention, the biassing force can be controlled by changing the pressure of control seal fluid by applying the pressure of the positive or negative control seal fluid in an axial direction of the revolving shaft of the mechanical seal. In operation as well as at rest, the control of the pressure or the gap between the sliding faces 2a, 3a can be achieved, too.
A fourth invention of the present application provides the mechanical seal in accordance with any of the first through third inventions, characterized in that it has a mechanism of supplying flushing liquid to the sliding rings 2, 3, that said controlling mechanism 6 controls biassing force by applying pressure of the control fluid to at least one sliding ring 3, and that the passage of control fluid in said controlling mechanism is independent of the passage for flushing liquid. With this invention, because the passage for control fluid is independent of the passage for flushing liquid, the pressure or the gap between the sliding faces 2a, 3a can be controlled irrespective of the flushing liquid. Flushing liquid is feared to leak on the seal fluid side in the agitating tank, and the passage for flushing liquid in the seal box may need cleaning and/or sterilization in accordance with CIP (cleaning in position) and/or SIP (sterilization in position). the provision of a passage for control fluid that is independent of the passage for flushing liquid and the breaking of communication between both passages may avoid the necessity of cleaning and sterilizing the passage for control fluid.
A fifth invention of the present application provides the mechanical seal in accordance with any of the first through fourth inventions, characterized in that said controlling mechanism 6 includes a piston 6 serving to move at least one sliding ring 3 to or away from the other sliding ring 2, so as to control biassing force by applying fluid pressure to said piston 6. In this invention, by exactly transmitting fluid pressure to the sliding rings via the piston 6, the reliable control of the pressure or the gap between the sliding faces 2a, 3a can be realized.
A sixth invention of the present application provides the mechanical seal in accordance with the fifth invention, characterized in that at least one sliding ring 3 is pressed by the elastic body toward the other sliding ring 2, and that the force of said elastic body may be transmitted to the one sliding ring 3 through said piston 6. In this invention, by transmitting combination of the pressure of the elastic body and the fluid pressure to the sliding rings via the piston 6, the reliable control of the pressure or the gap between the sliding faces 2a, 3a can be realized.
A seventh invention of the present application provides a mechanical seal comprising revolving shaft 1, sliding ring 2 which may rotate together with said revolving shaft 1, and sliding ring 3 disposed opposite to the sliding ring 2 in order to build a liquid seal between the sliding faces 2a, 3a of both sliding rings, characterized in that said controlling mechanism 53 comprises a first chamber 52 provided on the rear side of the sliding ring 3, a second chamber 54 enclosed by both sliding rings 2, 3 and revolving shaft 1, an orifice 53 acting to establish communication between said first and second chambers 52, 54, a first passage 51 of introducing fluid into the first chamber 52, and a second passage 55 of discharging fluid from the second chamber 54, and that the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings may be reduced or widened by dropping fluid pressure in the first chamber 52 to a lower level than that of fluid pressure in the second chamber 54 to let control fluid flow from the first passage 51 to the first chamber 52, the orifice 53, the second chamber 54, and the second passage 55 in this order. In this invention, the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings can be reduced or widened by the differential pressure between the first and second chambers 52, 54 with the orifice 53 contained by both chambers.
An eighth invention of the present application provides the mechanical seal in accordance with any of the first or seventh invention, characterized in that the control fluid also acts as flushing liquid, that the controlling mechanism 53 is embodied by orifice 53 formed in the passage for flushing liquid, and force directed toward the other sliding ring 2 is applied to the one sliding ring 3 by differential pressure caused by said orifice 53, and that the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings may be reduced or widened by changing the flow rate of the flushing liquid. The provision of the orifice 53 makes it possible to carry out the pressure control through a bigger amount of change than the change of the pressure of flushing liquid, and reverse of the differential pressure originated from the orifice 53 can also produce corresponding reverse of flushing liquid flowing in a direction of the orifice 53.
A ninth invention of the present invention provides the mechanical seal in accordance with any of the first through eighth inventions, characterized in that with the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings kept reduced or widened under the influence of said controlling mechanism 53, cleaning and sterilization of the sliding faces 2a, 3a may be achieved. In the mechanical seal, the sliding faces 2a, 3a of the sliding rings are usually stuck together. Therefore, the opposed sliding faces 2a, 3a were difficult to clean or sterilize unless disassembled. In this invention, however, by reducing or widening the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings using the controlling mechanism 53, fluid such as steam can be passed between the sliding faces 2a, 3a without process of disassembly, thereby enabling cleaning or sterilization of the sliding faces in just the state they usually are in.
A tenth invention of the present application provides an agitating device comprising revolving shaft 1 movable by power drive such as an electric motor 102, an agitating tank 103 of receiving the leading end of said revolving shaft 1, and an agitating member 105 provided on the leading end of said revolving shaft 1 received by the agitating tank 103, characterized in that the mechanical seal in accordance with any of the first through ninth inventions is located between the agitating tank 103 and the revolving shaft 1, and the one sliding ring of said mechanical seal is provided as sliding ring 3 on the agitating tank side while the other sliding ring is provided as sliding ring 2 on the revolving shaft side in such a manner that biassing force as adjusted by control fluid will be applied to any of both sliding rings.
In this invention, if change in pressure of fluid within the agitating tank occurred, the pressure or the gap between the sliding faces 2a, 3a of sliding rings can be controlled by the controlling mechanism of the mechanical seal. The sliding faces 2a, 3a can be also cleaned or sterilized together with the agitating tank without procedure for disassembly. Incidentally, the wording xe2x80x9cagitationxe2x80x9d used in the inventions of this application is a concept involving not only agitation itself but also mixing, emulsification, and dispersion.
An eleventh invention of the present invention provides the agitating device in accordance with the tenth invention, characterized in that said mechanical seal includes passages 51, 52, 53, 54, 55, 56, 57 for sterilization or cleaning, that said passages for sterilization or cleaning also act as passage for flushing liquid respectively, and that these passages are so inclined as to avoid formation of liquid pools therewithin, communicating with at least an inlet port 51a or outlet port 57a. 
In this invention, any formation of liquid pools or cold points within the passages can be prevented to ensure that reliable sterilization will be obtained.
A twelfth invention of the present application provides the agitating device in accordance with the eleventh invention, characterized in that the sliding ring 3 is provided on the wall 104 of the agitating tank 103, and the sliding ring 2 is provided on the leading end side of the revolving shaft 1 received by the agitating tank 103, so that the sliding ring 2 is positioned more inwardly of the agitating tank 103 than the sliding ring 3, whereby the biassing force adjusted by control fluid which is introduced from the outside of the agitating tank 103 is applied to the sliding ring 3.
In this invention, biassing force controlled by control fluid from the outside of the agitating tank 103 is applied to the sliding ring 3 on the fixed part, and the biassing force may be adjusted independent of the pressure inside the agitating tank 103, thereby controlling the pressure or the gap between the sliding faces 2a, 3a. 
A thirteenth invention of the present application provides a rotary apparatus including revolving shaft 1 movable by power drive such as electric motor 102, characterized in that the mechanical seal in accordance with any of the first through ninth inventions is used as a seal to prevent entry of liquid seal occurring around the revolving shaft 1.
The mechanical seal in accordance with the inventions of the present application is also usable with pumps or centrifugals in addition to the agitating device. In particular, if the mechanical seal is utilized in the rotary apparatus such as agitating device, pump, centrifugal, etc., workable in fluid passages which require CIP (cleaning in position) or SIP (sterilization in position), more reliable CIP (cleaning in position) or SIP (sterilization in position) can be put into practice. Even though CIP (cleaning in position) or SIP (sterilization in position) never takes place, it is useful to the control of the pressure between the sliding faces. Moreover, this specific mechanical seal is widely applicable to various kinds of rotary apparatus which need the provision of seal around the shaft or spindle, except the rotary apparatus as illustrated above.
A fourteenth invention of the present application provides an agitating process characterized in that when the agitating device in accordance with any of the tenth through twelfth inventions is used to agitate materials to be agitated in the agitating tank 103 of said agitating device, agitation is carried out with the sealability acceptable for the gap between the sliding rings 2, 3 retained at a higher level by urging control fluid forward and that if the mechanical seal is subjected to cleaning and sterilization when no agitation takes place, sterilizing liquid or cleaning liquid is passed through the sliding faces 2a, 3a of the opposed sliding rings with the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings kept reduced or widened by reducing the flow of control fluid or stopping the control fluid from flowing.
In this invention, the sterilization and cleaning fluids are passed between the sliding faces 2a, 3a of the opposed sliding rings with the pressure or the gap between the sliding faces 2a, 3a of the opposed sliding rings reduced to a low level or widened to ensure that the sliding faces 2a, 3a will be reliably cleaned and sterilized.